1. Field of the Invention
The present invention relates to a laser reflective mask and a fabrication method thereof. More particularly, the present invention relates to a laser reflective mask and a fabrication method thereof, in which reflective layers having different reflectances are sequentially and repeatedly laminated on top of a base substrate which has a reflective layer filling groove having a predetermined depth formed in a reflection region for a laser beam and then the remaining reflective layers laminated on the other regions except for the portion filled in the reflective layer filling groove are removed through a chemical mechanical polishing (CMP) process or a lift-off process using irradiation with the laser beam or an etchant, so that a reflective layer pattern configured to be filled in the reflective layer filling groove may be formed, thereby capable of not only facilitating a fabricating process of the laser reflective mask, but also forming a more precise pattern.
2. Description of the Related Art
Thin film technology refers to a film processing technique ranging from an atomic monolayer to a layer having a thickness of several micrometers (μm), and is used for electrode interconnection of an integrated circuit (IC), insulation between wires, fabrication of resistors, and the like. As a technology obtained by synthesizing the fabrication and application of thin films, the thin film technology has been widely used in industries of a semiconductor, a liquid crystal display (LCD), a solar cell, a light emitting diode (LED), and the like.
Products produced using the thin film technology are configured as various devices, and each of the devices is configured to have a structure necessary for its function by sequentially laminating several thin films.
The thin films are formed through a vacuum deposition, a sputtering, a thermal oxidation, or the like. Each of the thin films may be formed to have various structures through a patterning process.
The patterning process is generally performed by coating a photoresist on top of a substrate on which a layer to be etched is formed, performing an exposing process by irradiation with ultraviolet light through a mask having a desired pattern formed therein, forming a photoresist pattern through a developing process, forming a pattern of the layer to be etched by etching the layer to be etched using the photoresist pattern as an etching mask, and then removing the photoresist pattern.
Since the patterning process is very complicated, a long processing time is required to perform the patterning process. Since a high-priced photoresist is used in the patterning process, the processing cost increases. Since a multi-step process is performed, there occur various problems such as the existence of a potential defect factor and the reduction of productivity. Since various high-priced equipments are required to perform the multi-step process, the manufacturing cost increases. Since a large amount of chemical material is used in the patterning process, it contaminates the environment.
Meanwhile, a laser direct patterning (hereinafter, referred to as LDP) capable of patterning a thin film using a laser and an optical device has recently applied in various fields. The LDP has a patterning process simpler than the existing patterning process, and is low-priced and environmentally harmless.
The LDP is performed using a method of removing an unnecessary portion from a layer to be etched by irradiating the layer to be etched with a laser beam. In this case, the diameter of the laser beam is very small, and therefore, it takes much processing time to entirely pattern the layer to be etched, which is formed on a substrate.
To solve such a problem, a method is used, in which a mask having a desired pattern formed therein is disposed above the layer to be etched and the layer to be etched is patterned while a surface of the mask is scanned to be irradiated with the laser beam, thereby improving processing efficiency.
However, the mask used in such a process is generally formed by forming a shielding layer made of Cr or the like, which absorbs the laser beam, on top of a base substrate through which the laser beam may be transmitted and patterning the shielding layer through a patterning process using a photoresist. If the layer to be etched is etched by positioning the mask closely to the substrate, the mask is damaged due to the energy of the laser beam for etching the layer to be etched. Therefore, the layer to be etched is etched by interposing a projection lens for focusing the laser beam between the substrate and the mask, irradiating the mask with a laser beam having a slightly lower energy than that of the laser beam for etching the layer to be etched, and focusing the energy through the projection lens.
Therefore, the configuration of a patterning system is complicated due to the configuration of the mask described above, and the layer to be etched on the substrate is necessarily etched while moving an optical system which includes the substrate or the laser beam. Hence, it is difficult to implement a pattern having a desired shape due to the occurrence of an error according to the movement, and accordingly, there is a problem in that the productivity may be deteriorated.
To solve such a problem, U.S. Pat. No. 4,923,722 has disclosed a reflective mask that reflects a laser beam which is generated by repeatedly laminating a dielectric material having a relatively lower reflectance for the laser beam and a dielectric material having a relatively higher reflectance for the laser beam and collectively patterning the laminated dielectric materials using a photoresist.
FIG. 1 is a sectional view sequentially illustrating fabricating processes of a laser reflective mask according to a related art.
Referring to FIG. 1, a first reflective layer 122a having a lower reflectance and a second reflective layer 124a having a reflectance higher than that of the first reflective layer 122a are sequentially and repeatedly laminated on top of a substrate 110, through which a laser beam may be transmitted, to form a reflective layer 120a; a photoresist 130a is coated on top of the reflective layer 120a; and then the photoresist is irradiated with ultraviolet light using a mask 140 having a desired pattern formed therein (step a). Sequentially, the photoresist 130a is developed to form a photoresist pattern 130b (step b), and then the reflective layer 120a is etched using the photoresist pattern 130b as an etching mask to form a reflective layer pattern 120b (step c). Then, the photoresist pattern 130b is removed (step d), thereby forming the laser reflective mask.
However, in the fabricating processes described above, it is difficult to detect an etching end point due to the difference in etching rate between the first and second reflective layers 122a and 124a laminated on the substrate 110, so that it is difficult to control a pattern profile. Since the entire photoresist pattern 130b used as the etching mask is removed or separated while the reflective layer 120a is etched, the accuracy of the finally implemented reflective layer pattern 120b is degraded. Therefore, if the reflective layer pattern 120b is used as an etching mask, there is a problem in that it is difficult to etch a layer to be etched as a desired pattern shape.
To solve such a problem, a method has been used in which a hard mask using a metallic material such as gold is interposed between the reflective layer and the photoresist. However, since the hard mask has a poor adhesion with the reflective layer, the reflective layer may be separated while the reflective layer is etched. Therefore, there is a problem in that the accuracy of the patterns has been still degraded.